X-rays with characteristics of high brightness, low emittance and high coherence have become available in various wavelength ranges covering from soft X-rays to hard X-rays in third-generation radiation light facilities as typified by SPring-8. This has dramatically enhanced diverse analysis sensitivities and spatial resolutions in fluorescent X-ray analysis, photoelectron spectroscopic analysis, X-ray diffraction and the like. X-ray analysis and X-ray microscopic methods using such radiation light offer high sensitivities and resolutions and allow nondestructive observations, and therefore are currently being used in the fields of medicine, biology, material science and the like.
To add high spatial resolutions to various analysis techniques used with X-rays in radiation facilities, it is needed to collect X-ray nanobeams. In X-ray nanobeam formation, a reflective mirror is regarded as a most excellent light collection optical element, for the reason that there is no brightness or chromatic aberration. Generally used as a light collection optical system with a reflective mirror is a Kirkpatrick and Baez (K-B) mirror (refer to Patent Document 1). A K-B mirror arrangement is constituted by two full-reflective mirrors which have ellipsoidal forms with focal points at a light source and a collection point and collect light in vertical and horizontal directions, respectively.
A reflective mirror collects X-rays from a light source at a point by fully reflecting the X-rays or reflecting the X-rays with a multilayer film. To maintain a best light collection state, it is necessary to make constant an angle between incident X-rays and a mirror (incident angle), which would be changed due to temperature drifts. Most observations using radiation light require long-duration measurements, and it is therefore imperative to keep collected beams in a uniform state in an X-ray microscope using a light collection optical system with an X-ray mirror. This issue has been handled so far only by maintaining uniform temperature environments, which is deemed to be a major drawback in light collection optical systems using an X-ray mirror. A light collection method using an X-ray mirror has not been recognized to be suitable for long-duration observations due to this drawback, although in principle, this method is superior in aperture size and efficiency to other light collection methods using diffraction or refraction.    Patent Document 1: Japanese Unexamined Patent Publication No.